1. Field of the Invention
Polyoxyalkylene ether polyols, hereinafter for convenience called polyols, are commonly used in the production of urethane polymers. These polyols are reacted with polyisocyanate in the presence of added catalyst and other materials to produce urethane polymers which may be in the form of rubber-like elastomers, flexible or rigid foams and the like. In order that urethane polymers of desired properties and characteristics be produced, it is important that the polyols to be reacted with the polyisocyanate are essentially free of impurities which may function as undesirable catalysts or otherwise in the urethane polymer reaction.
Polyols, as commercially prepared, contain in the crude form various impurities such as alkali metal hydroxide, or other metal salts which were employed as catalysts for the production of polyols. The normal concentrations of catalysts range from 1700 to 4000 parts per million. It is desirable to reduce this to a level of about 5 parts per million or less.
2. Prior Art
Present commercial practices for the removal of these impurities can involve neutralization of the salts of acids forming insoluble salts and removal of same by filtration. Centrifugation, employing mixtures of polyol, water, and solvent can also be employed for the removal of residual catalyst. Ion exchange techniques have also been employed for the removal of catalysts.
The crude polyols without prior neutralization of the catalyst can be treated with a synthetic type adsorbent followed by filtration of the polyol. Present commercial practice involves mixing the polyol, adsorbent, water and optionally a filter aid then filtering off the polyol. The resulting adsorbent contains an amount of polyol equal to at least its own weight. The disposal of this spent adsorbent presents both ecological and safety problems. Generally, the polyols are not biodegradable and disposal in a landfill is not desirable. The wet adsorbent, if allowed to remain exposed to the atmosphere, becomes pyrophoric and creates a safety hazard. The loss of polyol results in increased product costs.
U.S. Pat. No. 3,433,816 teaches a process for separating mother liquor from a filter cake by employing a solvent. The prior art does not teach a process for the employment of a solvent to remove a polyol from a filter cake of synthetic aluminum silicate without removal of the adsorbed catalyst.
U.S. Pat. Nos. 2,425,845 and 2,448,664 teach neutralization of the alkaline catalyst with an acid followed by hot filtration for the removal of the residual catalyst.
There is no teaching in the prior art of the process of the instant invention.